Implementation of metal oxide films as oxide semiconductor films or conductive oxide films has been put into practical use through manufacturing with vacuum film formation methods, and is currently attracting attention.
An active area of research and development relates to the fabrication of oxide semiconductor films via a liquid phase process, with an object of forming an oxide semiconductor film having excellent semiconductor characteristics, simply, at low temperature, and under atmospheric pressure. A technique including coating a solution onto a substrate and using ultraviolet radiation has recently been published in which a thin film transistor (TFT) having a high carrier mobility is obtained at a low temperature of 150° C. or less (see Nature, 489, p. 128 (2012)).
On the other hand, a technique has been described for forming an oxide semiconductor precursor film using a solution of inexpensive nitrates, acetates, or the like (see International Publication (WO) 2009/081862).
Moreover, a method of manufacturing an oxide semiconductor film by forming a precursor film for an oxide semiconductor using a solution of nitrates, acetates, or the like, and irradiating the precursor film with an electromagnetic wave in the presence of oxygen has been described (WO) 2009/031381).
Moreover, a method of producing a metal oxide semiconductor has been described in which a thin film containing a precursor of a metal oxide semiconductor is formed by coating a solution including a nitrate or the like onto a substrate, subsequently heating the thin film to approximately 150° C. to allow the solvent to evaporate, and then irradiating the thin film with ultraviolet light in the presence of oxygen (see WO 2009/011224).
Moreover, a method of manufacturing a metal oxide semiconductor has been described in which a metal oxide semiconductor precursor film is formed by coating an aqueous metal oxide semiconductor precursor solution including a nitrate or the like onto a substrate, drying by evaporating the solvent at a temperature of from approximately 80° C. to approximately 100° C., and, after further heating to a temperature of from 50° C. to 200° C., converting the metal oxide semiconductor precursor film into a metal oxide semiconductor using an oxygen plasma method, a thermal oxidation method, a UV ozone method, or microwave heating (see Japanese Patent Application Laid-Open (JP-A) No. 2010-258057).